I am having the same problem after I upgraded to 2.0.5.
And the weird thing is that I only have the problem in Mac Firefox 2.0. I blew away all my cookies twice, also restarted my computer afterwards and it made no difference.
BUT, I can delete the posts fine if I log in with Safari.
Could it really be a permissions problem with the database if the problem is browser specific? That doesn’t seem to make sense to me (but hey… I’m only a designer, not a programmer.)
Atleast I have a workaround until this is fixed.